A mechanism for theT-odd pion fragmentation function

Abstract

We consider a simple rescattering mechanism to calculate a leading twist T-odd pion fragmentation function, a favored candidate for filtering the transversity properties of the nucleon. We evaluate the single spin azimuthal asymmetry for a transversely polarized target in semi-inclusive deep inelastic scattering ͑for HERMES kinematics͒. Additionally, we calculate the double T-odd cos 2 asymmetry in this framework.The transversity distribution h 1 ͑also known as ␦q), which measures the probability to find a transversely polarized quark in the transversely polarized nucleon, is as important for the description of the internal nucleon structure and its spin properties as the more familiar longitudinal distribution function g 1 . However, it still remains unmeasured, unlike the spin-average and helicity distribution functions, which are known experimentally and extensively modeled theoretically. The difficulty is that h 1 is a chiral-odd function, and consequently suppressed in inclusive deep inelastic scattering ͑DIS͒ processes ͓1͔; it has to be accompanied by a second chiral-odd quantity. In semi-inclusive deep inelastic scattering ͑SIDIS͒ of transversely polarized nucleons several methods have been proposed to access transversity distributions. The more promising one relies on the so called Collins fragmentation function ͓2͔, which correlates the transverse spin of the fragmenting quark to the transverse momentum of the produced hadron. In addition to being chiral odd, this fragmentation function is also time-reversal odd (T odd, see, e.g., ͓3,4͔͒, which makes its calculation challenging. Earlier, in addition to the Collins parametrization ͓2͔, a theoretical attempt was made to estimate the Collins function for pions ͓5͔. More recently, a nonvanishing T-odd fragmentation function was obtained through a consistent one-loop calculation, where massive constituent quarks and pions are the only effective degrees of freedom ͓6͔. In addition to parametrizations from data indicating a nonzero Collins function ͓7͔, the nonzero single spin asymmetries in recent measurements ͓8-10͔ signal the existence of a nontrivial T-odd effect. These indications of the T-odd fragmentation functions taken together call for deeper investigations, both theoretical and experimental.In this paper we explore an alternative one-gluon exchange mechanism, for the fragmentation of a transversely polarized quark into a spinless hadron similar to the approach we applied ͓11,12͔ to the distribution of the transversely polarized quarks in both the unpolarized and transversely polarized nucleons ͑in this context see also ͓13-15͔͒. Within this consistent framework we now make predictions for the leading twist T-odd pion fragmentation function, and the resulting single transverse-spin azimuthal asymmetry, sin(ϩ S ), as well as the spin-independent, cos 2, asymmetry in SIDIS.The nonperturbative information about the quark content of the target and the fragmentation of quarks into hadrons in SIDIS is encoded in the general form of the factorized cross sect...

Structure and spin of the nucleon

“…The beam SSA, first measured by CLAS collaboration [18] (see Fig. 2, right panel) have also been interpreted in terms of the Collins mechanism [36][37][38][39] and used for a first determination of the twist-3 distribution function e(x) [37]. The magnitude of the extracted e(x) is also consistent with predictions using the chiral quark soliton model [40][41][42].…”

Azimuthal and single spin asymmetries in hard scattering processes

“…All of them produce the necessary imaginary parts by adopting a simple model for the fragmentation process at tree level and inserting one-loop corrections. Two possibilities for the tree-level amplitudes and two possible kinds of one-loop corrections have been investigated, for a total of four different models: pseudoscalar pion-quark coupling with pion loops [177] and with gluon loops [179,174]; pseudovector pion-quark coupling with pion loops [178] and with gluon loops [180]. For gluon loop cases see Fig.…”

Quasi-Parton Distribution Functions: A Study in the Diquark Spectator Model

“…Within the framework of a spectator diquark model [17][18][19][20][21] we compute both the quasi-PDFs and the standard PDFs, to study/explore for what values of P z they are good approximations of each other. This can provide guidance for future lattice QCD calculations.…”